For purposes of fire protection, through holes, wall bushings and other openings in walls, floors and/or ceilings of buildings must be provided with fire-protection seals, so as to prevent fire and smoke from spreading out through these openings in the event of a fire. Such fire-protection seals may be used in the form of curable, formless fire-protection compositions or in the form of prefabricated strips, rings, panels and the like, which are introduced into the openings, which are to be sealed off, or with which these openings are covered.
Intumescing compositions for such fire-protection seals usually contain expandable graphite intercalation compounds, also known as expandable graphite, as intumescing fire-protection additive and are commercially available.
Intumescing, fire-protection compounds are compounds, which contain the following exogenous components (intercalates) intercalated between the lattice layers of the graphite. Such expandable, graphite intercalation compounds usually are produced by dispersing graphite particles in a solution, which contains an oxidizing agent and the guest compound, which is to be intercalated. Usually, nitric acid, potassium chlorate, chromic acid, potassium permanganate, hydrogen peroxide and the like are used as oxidizing agent. Concentrated sulfuric acid, for example, is used as a compound, which is to be intercalated, the reaction being carried out at a temperature from 60° to 130° C. for up to four hours (see, for example, EP-B-0 085 121). Alternatively, it is also possible to intercalate metal chlorides in the graphite in the presence, for example, of chlorine gas (E. Stumpp, Physica (1981), 9-16).
A further method for producing such sulfuric acid-graphite particles is known, for example, from U.S. Pat. No. 4,091,083. The method includes dispersing crystalline graphite particles in sulfuric acid, stirring the mixture with the addition of hydrogen peroxide and continuing the stirring until the sulfuric acid has been intercalated in the graphite. Subsequently, the excess acid is separated, the remaining acid, present in the solid product, is removed by washing repeatedly with water and the material is dried.
When heated to a temperature above the so-called onset temperature, the expandable graphite intercalation compounds or expandable graphite expand greatly with expansion factors of more than 200. The expansion is caused owing to the fact that the compounds, intercalated in the layer structure of the graphite, are decomposed by the rapid heating to this temperature with the formation of gaseous materials, as a result of which the graphite particles are expanded perpendicularly to the layer plane (EP-B-0 085 121).
This expansion behavior is utilized in intumescing compositions, which are used, for example, for the fire-protection sealing of cable and pipe wall bushings through walls and ceilings of buildings. In the event of a fire, the graphite particles expand when the onset temperature is reached, as does the intumescing composition sealing the wall bushing, so that, even if the cable and/or plastic pipe passed through the wall bushing has burned away, the fire is prevented or delayed from breaking through the wall bushing.
For the fire-protection sealing of through holes, wall bushings and other openings in walls, floors and/or ceilings of buildings, it is now possible, on the one hand, to introduce the fire-protection seal into the opening, such as an annular gap, about a plastic pipe passed through the wall, as shown in FIG. 1a of the attached drawing, or to provide it in the form of a covering on the wall, as shown in FIG. 1b. Problems arise in the remaining annular gap if the fire-protection seal is provided as a compartmentalization, as shown in FIG. 1a. or if the fire protection seal is covered by the building construction, owing to the fact that, in this case, the heat input in the event of a fire, by means of which the expansion of the intumescing fire-protection additive in the fire-protection composition is initiated, is accomplished over a relatively small surface, namely the front side of the fire-protection sealing, present in the annular gap, in the case of FIG. 1a), whereas, in the case that the fire-protection seal is applied on the wall, the intumescing fire-protection composition is exposed to the high heat of the fire over a large area.
Since plastic pipes, for example, which are passed through the wall bushing, collapse almost equally rapidly in both cases in the event of a fire, problems arise in the event that the fire-protection composition is introduced into the opening itself owing to the fact that, if the sealing material, present in the opening, collapses before the onset temperature of the intumescing fire-protection composition is reached, fire and smoke can break through the opening.
This is the case especially with conventional, intumescing fire-protection seals, which contain the usually employed, expandable graphite as intumescing fire-protection additive, since the characteristic values of the expansion behavior of the latter are not satisfactory especially for this application. In this connection, the characteristic values are the onset temperature of the expandable graphite, that is, the temperature, at which the expansion of the particles of the expandable graphite commences. Furthermore, the expansion rate in the region of the onset temperature, the maximum attainable expansion volume and the average expansion coefficient are important. Reference is made further below to precise definitions for determining these expansion parameters.
According to the state of the art, commercially obtainable sulfuric acid-graphite particles are used predominantly as intumescing fire-protection additives in such intumescing fire-protection seals, which have an onset temperature of 200° C. Admittedly, modified sulfuric acid-graphite particles are also obtainable commercially, which have a low onset temperature of 150° C. or 160° C., however, they are not satisfactory with respect to the expansion volume and the expansion rate. The expansion parameters of two typical, commercial, expandable graphite types are listed in the following Table 1:
TABLE 1Expansion parameters of two typical, commercial,expandable graphite types (particle size250-400 μm, isolated by dry screening)SulfuricSulfuric acidAcidNitric acidGraphiteGraphiteOnset (° C.)200160Volume or sample weight in %/mg245192T100 in ° C.361268Rate in the onset 1 range in %/° C.813Rates between onsets 1 and 2%/° C.—3Rate in the onset 2 range in %/° C.—29Average expansion coefficient between0.090.11TMA onset 1 and T100 in K−1
It has now turned out that, when such commercial, expandable graphites are used and the fire-protection seal is introduced into the interior of the openings that are to be closed off, the expansion parameters of the conventional commercial expandable graphites are not adequate for the, in this case, small heat input, to initiate the intumescence of the fire-protection seal sufficiently rapidly and to achieve a corresponding increase in volume, so that fire-protection sealing is ensured even if the plastic pipe, passed through the opening, collapses.